Navegando por Autor "Melo, C. H. F."

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Incidence of planet candidates in open clusters and a planet confirmation
(EDPSCIENCE, 2018-12-10) Martins, Bruno Leonardo Canto; Leão, I. C.; Alves, S.; Oliveira, G. Pereira de; Cortés, C.; Brucalassi, A.; Melo, C. H. F.; Freitas, D. B. de; Pasquini, L.; Medeiros, J. R. de
Context. Detecting exoplanets in clusters of different ages is a powerful tool for understanding a number of open questions, such as how the occurrence rate of planets depends on stellar metallicity, on mass, or on stellar environment. Aims. We present the first results of our HARPS long-term radial velocity (RV) survey which aims to discover exoplanets around intermediate-mass (between ∼2 and 6 M ) evolved stars in open clusters. Methods. We selected 826 bona fide HARPS observations of 114 giants from an initial list of 29 open clusters and computed the halfpeak to peak variability of the HARPS RV measurements, namely ∆RV=2, for each target, to search for the best planet-host candidates. We also performed time series analyses for a few targets for which we have enough observations to search for orbital solutions. Results. Although we attempted to rule out the presence of binaries on the basis of previous surveys, we detected 14 new binary candidates in our sample, most of them identified from a comparison between HARPS and CORAVEL data. We also suggest 11 new planet-host candidates based on a relation between the stellar surface gravity and ∆RV=2. Ten of the candidates are less than 3 M , showing evidence of a low planet occurrence rate for massive stars. One of the planet-host candidates and one of the binary candidates show very clear RV periodic variations, allowing us to confirm the discovery of a new planet and to compute the orbital solution for the binary. The planet is IC 4651 9122b, with a minimum mass of m sin i = 6:3 MJ and a semimajor axis a = 2:0 AU. The binary companion is NGC 5822 201B, with a very low minimum mass of m sin i = 0:11 M and a semimajor axis a = 6:5 AU, which is comparable to the Jupiter distance to the Sun.
Lithium abundances and extra mixing processes in evolved stars of M 67
(Astronomy & Astrophysics, 2011) Martins, B. L. Canto; Lèbre, A.; Palacios, A.; Laverny, P. de; Richard, O.; Melo, C. H. F.; Nascimento Jr, J. D. do; Medeiros, José Renan de
Aims. We present a spectroscopic analysis of a sample of evolved stars in M 67 (turn-off, subgiant and giant stars) in order to bring observational constraints to evolutionary models taking into account non-standard transport processes. Methods. We determined the stellar parameters (Teff, log g, [Fe/H]), microturbulent and rotational velocities and, lithium abundances (ALi) for 27 evolved stars of M 67 with the spectral synthesis method based on MARCS model atmospheres. We also computed non-standard stellar evolution models, taking into account atomic diffusion and rotation-induced transport of angular momentum and chemicals that were compared with this set of homogeneous data. Results. The lithium abundances that we derive for the 27 stars in our sample follow a clear evolutionary pattern ranging from the turn-off to the Red Giant Branch. Our abundance determination confirms the well known decrease of lithium content for evolved stars. For the first time, we provide a consistent interpretation of both the surface rotation velocity and of the lithium abundance patterns observed in an homogeneous sample of TO and evolved stars of M 67. We show that the lithium evolution is determined by the evolution of the angular momentum through rotation-induced mixing in low-mass stars, in particular for those with initial masses larger than 1.30 M when at solar metallicity.
Overview of semi-sinusoidal stellar variability with the CoRoT satellite
(Astronomy & Astrophysics, 2013) Medeiros, José Renan de; Lopes, C. E. Ferreira; Leão, Izan de Castro; Martins, Bruno Leonardo Canto; Catelan, M.; Baglin, A.; Vieira, S.; Bravo, J. P.; Cortés, C.; Freitas, D. B. de; Janot-Pacheco, E.; Maciel, S. C.; Melo, C. H. F.; Osorio, Y.; Mello, G. F. Porto de; Valio, A.
Context. To date, the CoRoT space mission has produced more than 124 471 light curves. Classifying these curves in terms of unambiguous variability behavior is mandatory for obtaining an unbiased statistical view on their controlling root-causes. Aims. The present study provides an overview of semi-sinusoidal light curves observed by the CoRoT exo-field CCDs. Methods. We selected a sample of 4206 light curves presenting well-defined semi-sinusoidal signatures. The variability periods were computed based on Lomb-Scargle periodograms, harmonic fits, and visual inspection. Results. Color–period diagrams for the present sample show the trend of an increase of the variability periods as long as the stars evolve. This evolutionary behavior is also noticed when comparing the period distribution in the Galactic center and anti-center directions. These aspects indicate a compatibility with stellar rotation, although more information is needed to confirm their rootcauses. Considering this possibility, we identified a subset of three Sun-like candidates by their photometric period. Finally, the variability period versus color diagram behavior was found to be highly dependent on the reddening correction.
S1242: a lithium-rich subgiant star in the open cluster M 67
(Astronomy & Astrophysics, 2006-05-04) Martins, B. L. Canto; Lèbre, A.; Laverny, P. de; Melo, C. H. F.; Nascimento Jr, J. D. do; Richard, O.; Medeiros, José Renan de
Aims. We report the serendipitous discovery of a lithium-rich subgiant star, S1242. This object is member of a large eccentricity spectroscopic binary system in the solar-age open cluster M 67. Methods. Using VLT/FLAMES-UVES observations and synthetic spectrum analysis, we derived for this star stellar parameters (temperature, gravity, metallicity and rotational velocity) and a surface Li abundance (ALi = 2.7) larger than the higher abundance of M 67 stars near the turn-off. Results. The high Li abundance we found in S1242 points to an excess of lithium at the subgiant stage. We discuss two possible explanations for this unusually high Li content in this binary system: a preservation of the Li at the turn-off stage due to tidal effects, or an efficient dredge-up of Li, hidden below the convective zone by atomic diffusion occuring in the post turn-off stage.
S1242: a lithium-rich subgiant star in the open cluster M 67
(EDP Sciences, 2005-12-29) Martins, B. L. Canto; Lèbre, A.; de Laverny, P.; Melo, C. H. F.; Nascimento Júnior, José Dias do; de Medeiros, J. R.
Aims.We report the serendipitous discovery of a lithium-rich subgiant star, S1242. This object is member of a large eccentricity spectroscopic binary system in the solar-age open cluster M 67. Methods.Using VLT/FLAMES-UVES observations and synthetic spectrum analysis, we derived for this star stellar parameters (temperature, gravity, metallicity and rotational velocity) and a surface Li abundance () larger than the higher abundance of M 67 stars near the turn-off. Results.The high Li abundance we found in S1242 points to an excess of lithium at the subgiant stage. We discuss two possible explanations for this unusually high Li content in this binary system: a preservation of the Li at the turn-off stage due to tidal effects, or an efficient dredge-up of Li, hidden below the convective zone by atomic diffusion occuring in the post turn-off stage

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Navegando por Autor "Melo, C. H. F."